The present invention relates to pressure sensors of the type used to measure the pressure of a process fluid. More specifically, the present invention relates to compensating for inaccuracies in a differential pressure measurement due to a line pressure.
Transmitters are used in process monitoring and control systems to measure various process variables of industrial processes. One type of transmitter measures pressure of process fluid in the process. Various techniques have been utilized in pressure sensors used in such transmitters. One well known capacitive measuring technique is to use a deflectable diaphragm. A capacitance is measured between two opposing surfaces, with the diaphragm forming one of the capacitive plates of the capacitor and another fixed electrode typically attached to the body of the sensor forming the second capacitor plate. As the diaphragm is deflected due to applied pressure, the measured capacitance changes. In such a configuration, there are a number of sources of inaccuracies in pressure measurements.
One technique which addresses these inaccuracies is set forth in U.S. Pat. No. 6,295,875 entitled, “PROCESS PRESSURE MEASUREMENT DEVICES WITH IMPROVED ERROR COMPENSATION” issued Oct. 2, 2011 to Frick et al. which is incorporated herein by reference in its entirety. This patent describes a differential pressure sensor that includes an additional electrode for use in reducing measurement inaccuracies. However, in some instances a line pressure applied to the pressure sensor can introduce inaccuracies in the measured differential pressure.